J. Perez-Silva

Ultrastructural and cytochemical study of the encystment in the Hypotrichous ciliate Histriculus similis

Summary Electron microscopic observations during the encystment of Histriculus similis confirmed that the cyst wall, composed of four layers, is derived from different kinds of precursors which are synthesized de novo. The ectocyst precursors are composed of stacked plates enclosed in a unit membrane. The mesocyst precursors are fibrous packets of variable shapes and sizes. The granular layer precursors are vesicles of different sizes and shapes surrounded by a unit membrane. A cytochemical and enzymatic study has been carried out to determine the cytochemical composition of the cyst wall precursors and their origin.

Inter and intraspecific transfer of a Rhizobium fredii symbiotic plasmid: expression and incompatibility of symbiotic plasmids

Summary The Rhizobium fredii symbiotic plasmid pRfr193a has been marked by Tn5-Mob insertion and transferred to Rhizobium sp. ( Hedysarum coronarium ) strain IS123 and to a Fix - mutant derivative (AB-24) of R. fredii strain USDA 194. Most of the IS123 transconjugants carrying pRfr193a::Tn5-Mob (pAB1) nodulated ineffectively on Glycine max and all of them failed to nodulate on H. coronarium . These transconjugants had lost the indigenous IS123 symbiotic plasmid (pRHcRB16b) and showed an additional plasmid band. Transfer of the R. fredii symbiotic plasmid pAB1 to R. fredii strain AB-24 did not correct the Fix - phenotype of the recipient strain.

Polysaccharides and lipopolysaccharides and infectivity of Rhizobium trifolii

Abstract The extracellular polysaccharides obtained from infective and noninfective strains of Rhizobium trifolii were analysed to investigate if infective properties were correlated with polysaccharide composition. The results indicate that soluble extracellular polysaccharides were not a determinant factor in infectivity. However, electrophoresis of bacterial surface lipopolysaccharides showed a relation between the loss of infectivity and changes in electrophoretic mobility.

Morphology of Frontonia betica Arroyo & Pérez-Silva 1977 (Ciliophora, Peniculida)

Summary Frontonia betica was isolated from water samples collected at several sites in the Bajo Guadalquivir Valley. This species presents the following morphological characteristics: The ellipsoid body measures between 260–450 μm in length, presents 160–180 somatic kineties, with those on the ventral side not bipolar and most of them converging at the postoral suture. The peniculi P1, P2 and P3 measure about 47, 44 and 39 μm, respectively and each of them consists of four rows of kinetosomes. There are three vestibular kineties, one or two contractile vacuoles, and the nuclear apparatus consists of an ellipsoid macronucleus surrounded by 5–10 spherical micronuclei.